In my case, my first two dynohubs were for touring bikes I was building up from parts. Thus, the cost was only the dynohub cost minus the cost of the non-dyno hub that I otherwise would have bought. But if you have a complete bike with a good front wheel, then the cost of a dynohub is much greater.

I was not anticipating using a dynohub for lighting much, I wanted a way to charge up batteries when I was on a bike tour and rarely had access to an outlet to plug into. But once I had the dynohub wheels, I figured I might as well put a couple lights on too.